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"A thousand terrorists have been killed, 50 motorised canoes have been destroyed," the colonel said, referring to a large boat also called a pirogue.

Agouna said the operation, which was launched after nearly 100 soldiers were killed in a Boko Haram attack last month, ended on Wednesday after the armed fighters were forced out of the country.

It is the first official snapshot of the outcome of Operation Bohoma Anger, launched after at least 92 soldiers were killed on March 23 in the deadliest-ever attack by Boko Haram on the country's military forces. The armed group had mounted a seven-hour assault on a Chadian army base at Bohoma.

Reporting from the Nigerian capital, Abuja, Al Jazeera’s Ahmed Idris said: "The country is trying to help other regional powers and regional forces under a group called the Multinational Joint Task Force (MNJTF) to finally defeat the Boko Haram."

"A similar operation was conducted five years ago, in 2015, that decimated the Boko Haram population. They have regrouped since then, and attacked and killed several thousands in the process and regional armies in the Lake Chad area have been struggling to deal with the problem," Idris added.

Lake Chad is a vast, marshy body of water where the borders of Niger, Nigeria, Chad and Cameroon meet.

The western shores of the lake have been hit by armed fighters crossing from northeastern Nigeria, where Boko Haram launched a bloody campaign of violence in 2009.

'Shouldering all the burden'

Chad declared departments near the lake "a war zone" in order to give the military free rein for the offensive.

The four countries bordering the lake in 2015 set up the MNJTF, also including Benin, to fight Boko Haram.

But Chad, whose forces have a relatively high standing in the Sahel region, has shown frustration with the MNJTF following the Bohoma losses.

"Chad is alone in shouldering all the burden of the war against Boko Haram," President Idriss Deby said last weekend.

"It is not clear if this will be the end or the beginning of the end of Boko Haram in the region. Many experts believe it is going to be very very difficult to say that Boko Haram is defeated or will be defeated anytime soon because this is an idealogy that has taken foothold for more than a decade in Nigeria which is spilling into its neighbours," Al Jazeera's Idris added.

Separately, in Niger, the defence ministry in Niamey said its armed forces, in a joint operation with Chad, had inflicted "heavy losses" on Boko Haram in the lake region.

"Arms caches, logistical points and several boats were destroyed" and islands used as rear bases in the lake's marshland were "bombarded from the air," it said.

Landlocked Niger is facing attacks by armed group on opposite ends of the country - fighting that has spilled over from neighbouring Mali, and raids in the Lake Chad region by Boko Haram fighters.

Boko Haram's 11-year-old campaign has claimed tens of thousands of lives in northeast Nigeria and driven nearly two million people from their homes.